To preserve a tooth that has or could develop a diseased pulp cavity, it is necessary to prevent bacterial proliferation within the root or pulp canal of the tooth by enlarging the canal without excessively weakening the root's wall by using endodontic files, bores, reamers or other instrumentation in order to: 1) mechanically remove as much of the root canal contents as is possible and 2) allow the introduction of irrigants into the root canal space that dissolve and disinfect organic debris, thus minimizing the presence of bacteria, as well as clearing the walls of the root canal of calcific debris created during instrumentation. After completing steps 1 and 2, the root canal is typically filled or obturated with a material such as gutta-percha and a sealer to occlude the pulp cavity and thus seal the root canal. This procedure is referred to as root canal therapy. Irrigation assists in removing debris and necrotic material remaining after the endodontic files, bores, and reamers used during the removing and shaping steps of the procedure. Although, the irrigant preferably is capable of dissolving or disrupting soft tissue remnants to permit their removal, the irrigant may be any suitable liquid such as water or various alcohols. More particularly, although some degree of debridement is preferred, any fluid may be used to flush debris from the root canal. General examples of appropriate irrigants include hydrogen peroxide and sodium hypochlorite. In order to ensure that as much of the debris and necrotic material as possible is removed, the irrigant is typically applied under pressure using a syringe and a needle inserted into the canal as shown in FIG. 2. However, as reported in Endodontics, 5.sup.th Edition, by John I Ingle and Leif K Bakland published June 2002, pages 502-503, it is important that the needle fit loosely in the canal to allow backflow. It is also reported that there is little flushing beyond the depth of the needle unless the needle is bound in the canal and the irrigant forcibly ejected which is undesirable due to the danger of an irrigant such as sodium hypochlorite breaching the apex of the canal and entering the periapical tissue. However, unless the end of the needle is near the apex, the portion of the canal from the apex to the end of the needle cannot be effectively irrigated. But placing the end of the needle near the apex increases the likelihood of the irrigant, which is applied under pressure, entering the periapical tissue. This can be a source of post treatment endodontic pain for the patient. Furthermore, if a significant quantity of an irrigant like sodium hypochlorite is accidentally injected into the periapical tissue, morbid clinical complication can occur including excruciating pain, immediate swelling (ballooning) of the tissue and profuse bleeding.
Existing techniques attempt to address this problem by using very small needles to get close to the apex while still fitting loosely in the canal to allow backflow or using an instrument to move some of the irrigant towards the apex with the irrigant no longer under pressure. However, neither technique completely solves the problem. Even the tip of the smallest needles that deliver irrigants under pressure must be kept a safe distance (approximately 4-6 mm) away from the apex in order to avoid accidentally forcing irrigants into the periapical tissue. This safety issue most often results in an area or zone between the apex and needle tip devoid of irrigant. Use of an instrument to force the irrigant through this zone towards the apex is very time consuming and also does not guarantee that the irrigant has flushed the canal all the way to the apex without going too far.